Moulding machine adapted for plasticising a thermo-plastic material or a thermo-setting material which is subsequently to be moulded



Aug. 6, 1957 w 2,802,084

MOULDING MACHINE ADAPTED FOR PLASTICISING A THERMO-PLASTIC MATERIAL OR A THERMO-SETTING MATERIAL WHICH IS SURSEQUENTLY TO BE MOULDED Filed Dec. 21, 1955 2 Sheets-Sheet 1 0h. MAR/(LEW 6, 1957 c. K. MARKLEW 2,802,084

MOULDI NG MACHINE ADAPTED FOR PLASTICISING A THERMO-PLASTIC MATERIAL OR A THERMO-SETTING MATERIAL WHICH IS SUBSEQUENTLY TO BE MOULDED Filed Dec. 27, 1955 2 Sheets-Sheet 2 CKMARKZZW Afr/ United States Patent MOULDING MACHINE ADAPTED FOR PLASTI- CISING A THERMO-PLASTIC MATERIAL OR A THERMO-SETTING MATERIAL WHICH IS SUB- SEQUENTLY TO BE MOULDED Cecil K. Marklew, Coventry, England, assignor to Alfred A Herbert Limited, Coventry, England Application December 27, 1955, Serial No. 555,661

7 Claims. (Cl. 219-1051) This invention relates to a moulding machine, adapted for plasticising a thermoplastic materialor a thermosetting material which is subsequently to be moulded,

- including an alternating current induction heating appa- -(e. g., 22 gauge) and low specific resistance (e. g., 1.66

microohms per cubic centimetre), through which an alternating current, at a voltage of 200 to 250, is passed to induce eddy currents in the body and produce heating thereof.

With known insulating materials of a nature suitable for insulating the wire, it is found that degeneration of the insulation occurs when the body is heated to above 300 C., due to heat conducted to the coils. Also at these temperatures the copper oxidizes rapidly when the insulation degenerates, and, due to the then increased resistance of the wire, local overheating is produced and the wire burns out. This situation is also aggravated by the small cross-section of the wire necessitated by the large number of turns.

The object of the invention is to mitigate these disadvantages. 1

According to the invention, a moulding machine, adapted for plasticising a thermo-plastic material or a thermo-setting material which is subsequently to be moulded, includes an electrical induction heating apparatus operable at normal power frequencies (e. g., 50 c./s. or 60 c./s.) the heating apparatus comprising a ferrous metallic body having wound on it a naked metallic strip forming a heater coil, or coils, the coil or coils being arranged in a single bank and insulated from the ferrous metallic body by a layer of refractory material having an electrical resistance at least adequate to insulate the coil from the body at the low voltage employed.

It is to be understood that by low voltage is meant a voltage of the order of 0 to 15 volts, as distinct from voltages of the order of 200 to 250 volts hitherto employed.

One embodiment of the invention is hereinafter particularly described with reference to the accompanying drawings in which:

Figure 1 is an elevation, partly in section, of a moulding machine embodying the present invention and adapted for plasticising a thermo-plastic material or a thermosetting material which is subsequently to be moulded;

Figure 2 is a section on the chain line in Figure I seen in the direction indicated by the arrows 22 in that figure; and

Figure 3 is a section on the said chain line of Figure 1 but looking in the direction of the arrows 33.

In the drawings a heating cylinder 11 has a flange 12 to which is secured, by a ring of bolts 13, a fitting 14 for attachment to a hopper (not shown) from which is supplied a particulate thermo-plastic material to be plasticised and afterwards fed (e. g., by a hydraulicallyoperated ramnot shown-in the cylinder) through a nozzle 15 into a mouldalso not shown.

The cylinder 11 is covered by a refractory, insulating layer 16 (e. g., of asbestos tape), and the heating coil is wound to engage this layer.

Two of such heating coils are shown, one being indicated at 17 and for producing a high heat output so as quickly to plasticize the material entering the cylinder, and the other being indicated at 18 and having for its purpose to provide a lower heat output for maintaining the material in plastic condition until it is fed through the nozzle 15 and into the mould.

Each of these coils is of naked nickel (of specific resistance 11.8 microohms per cubic centimetre) and is of large, rectangular cross-section (e. g., V by A"), being held in position on the layer 16 by metal bars 19 which have an insulating surface 20 contacting the coils and are made fast with the cylinder 11 by screws 21 and locknuts 22. It will be observed that the turns of both coils are widely spaced and that the screws 21 extend clear between them.

In the example shown, the flange 12 is inductively heated by a volute coil 23 of an insulated conductor having a rectangular cross-section.

The coils 17 and 18 have earthing connections 17a, 18a at their one ends to the cylinder 11, and one end of the coil 23 has an earthing connection 23a to the flange 12, which latter has secured to it, by' a nut and bolt 24, 25 a socket 26 for the appropriate lead 27 of a transformer (not shown). Each of the earthing connections is in the form of a conductive plate which is held in clamping relationship to the naked conductors of the coils 17 and 18, or to a bared end portion of the coil 23', by conductive screws 28 engaging in the cylinder, or flange, as appropriate.

The opposite ends of the coils 17 and 23 are jointly clamped by nuts and bolts 29, 30 (one only of which can be seen) between jaws of a common socket 31 for a supply lead 32 from the transformer, and, as shown by Figure 1, the other end of the coil 18 is fed, from another supply tapping 33 from the transformer, through a socket 34 in which the said other end is clamped by screws 35, 35.

Although reference has been made to a single transformer it is convenient to use two continuously rated transformers embodied in a single, air-cooled unit. One of these, for example, could be rated at 4.5 kva. and the other at 2.5 kva., and both have an input supply of 230 volts at 50 cycles. The larger transformer would be the one supplying the coils 17 and 23 (e. g., to generate a temperature in the cylinder of, say, 350 C.), and the smaller one would supply the coil 18 to generate a temperature in the cylinder of, say, 300 C.these temperature figures, of course, depending on the material to be plasticized. Each of these transformers could have primary tappings to give alternative secondary outputs at, say, 4, 4.5, 5, 5.5 and 6 volts so as to enable the temperatures of the coils 17, 18 and 23 to be adjusted when a different material is to be treated.

Temperature control of the treatment can be obtained in a usual way, such, for instance, as by thermo-couples associated with the cylinder and flange and actuating switches for selecting the primary tappings of the transformers.

The cylinder and coils, as a unit, are preferably lagged for conserving heat, and such a lagging (e. g., of a kind used for steam pipes) is shown at 36 in Figure 1, being omitted for the sake of clearness from the other figures.

In an alternative embodiment of the invention the heating apparatus is in the form of a coil wound round part of a platen with a layer of refractory insulating material between the coil and the platen.

The platen being metallic forms the body which is to be heatedby the coil, and can be used to support one portion of a die in which thermo-setting material is to be heated so as to plasticise the material prior to moulding.

Alternatively, or additionally, the coilcan-be wound round part of the die through channels in the lower portion of the die, the die itself forming the, or part of the, said body.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A moulding machine, adapted for plasticising a thermoplastic material or a thermo-setting material which is .subsequently to be moulded, includingan alternating current induction heating apparatus operable at normal power frequencies, the heating apparatus comprising a said body, and a naked strip of a metal having a high specific resistance and resistance to oxidation wound in a single bank of spaced turns, directly on said refractory material and forming a heater coil, said heater coil to be supplied at low voltage, and said refractory material having an electrical resistance at least adequate to insulate said coil from said body. 7

2. A moulding machine, adapted for plasticising a thermo-plastic material which is subsequently to be ferrous metallic body, a layer of refractory material on moulded, including an alternating current induction heating apparatus operable at normal power frequencies, the heating apparatus comprising a ferrous metallic cylinder for containing the material, a layer of refractory material on said cylinder, and a naked strip of a metal having -a high specific resistance and resistance to oxidation wound in. a single bank of spaced turns, directly on said refractory material and forming a heater coil, said heater coil to be supplied at low voltage, and said refractory material having an electrical resistance at least adequate to insulate said coil from said cylinder.

3. A moulding machine, adapted for plasticising a thermo-setting material which is subsequently ,to be moulded, including an alternating current induction heating apparatus operable at normal power frequencies, the heating apparatus comprising a ferrous metallic body, said body comprising a platen for supporting a die, a layer of refractory material on said platen, and a naked strip of a metal having a high specific resistance and resistance to oxidation wound in a single bank of spaced turns, directly on said refractory material and forming a heater coil, said heater coil to be supplied at low voltage, and said refractory material having an electrical resistance at least adequate to insulate said coil from said platen.

.4. A moulding machine, adapted for plasticising a vthermo-plastic material or a thermo-setting material which is subsequently to be moulded, including an alternating current induction heating apparatus operable at normal power frequencies, the heating apparatus com- 1 prising a ferrous metallic body, a layer of refractory material on said body, and two naked strips of a metal having a high specific resistance and resistance to oxidation wound 'on said refractory material, said strips wound directly on said material in axially-spaced relationship in single banks of spaced turns and forming separate heater coils, said heater coils adapted to be supplied separately at ditferent low voltages, and said refractory material having an electrical resistance at least adequate to insulate said coils from said body.

5. A moulding machine, adapted for plasticising a thermo-plastic material or a thermo-setting material'which is subsequently to be moulded, including an alternating current induction heating apparatus operable at normal power frequencies, the heating apparatus comprising a ferrous metallic body, a layer of refractory material on said body, anda naked metallic strip. Wound with widely spaced turns in a single bank directly on said refractory material and forming a heater coil, a plurality of rigid insulating bars, said bars arranged in:a circle outside said heater coil and-with their major, dimension directed axially of the latter, screws extending through said bars and the spaces between said turns and into said body to locate said heater coil, said heater coil to be supplied at low voltage, and said refractory material having an electrical resistance at least adequate to insulate said coil from said body. p q 1 6. A moulding machine, adapted for plasticising a thermo-plastic material or a thermo-setting material which is subsequently to be moulded, including an alternating current induction heating apparatus operable at normal power frequencies, the heating apparatus com} prising a ferrous metallic body, a layer of refractory material onsaid body, a naked metallic strip wound in a single bank of spaced turns directly on said refractory material and forming a heater coil, and lagging covering said body and heater coil, said heater coil to be supplied at low voltage, and said refractory material having an electrical resistance at least adequate to insulate saidcoil from said body.

7. A moulding machine, adapted for plasticising a thermo-plastic material or a thermo-setting material which is subsequently to be moulded, including an alternating current induction heating apparatus operable at normal power frequencies, the heating apparatus comprising a ferrous metallic body, said body havinga radially-extending part, a layer of refractory'material on said body, a naked metallic strip wound in a single bank of spaced turns directly on said refractory material and forming a heater coil, and a volute induction-heating coil abutting said radially-extending part, said heater coils to References Cited in the file of this patent UNITED STATES PATENTS "2,226,447 Smith et al. Dec. 24, 1940 2,226,448 .Smith Dec. 24, 1940 2,729,731 'Kleinpeter Jan. 3, 1956 

